In a communication using the Ethernet (Registered trademark), flexibility of a physical link which can be used in a network is lost due to Spanning Tree Protocol (STP), and accordingly a multi-path communication has become gradually impossible.
In order to solve the problem, a route control by the OpenFlow is proposed (reference to Non-Patent Literature 1). A computer system using the OpenFlow technique is disclosed, for example, in JP 2003-229913A (Patent Literature 1). A network switch corresponding to the technique (hereinafter, to be referred to as a programmable flow switch (PFS)) retains detail information such as a protocol type and a port number in a flow table, and can control a flow. It should be noted that the PFS is also referred to as an OpenFlow switch.
FIG. 1 is a diagram showing an example of a configuration of the computer system using the OpenFlow technique. Referring to FIG. 1, a programmable flow controller (PFC, to be referred to as an open flow controller) 100 sets a flow entry to the PFSs 200 and 300 in a single subnet (a P-Flow Network), to perform a flow control in the subnet.
Each of the PFSs 200 and 300 refers to its flow table to execute an action (for example, relay and discard of a data packet) defined in the flow entry, and corresponding to header information of a received packet. Specifically, when a packet transferred between HOSTs 400 is received, each of the PFSs 200 and 300 executes the action defined in the flow entry, if the header information of the received packet conforms to (match to) (a rule of) the flow entry set in its own flow table. On the other hand, when the header information of the received packet does not conform to (match to) (the rule of) the flow entry set in the flow table, each of the PFSs 200 and 300 recognizes the received packet as a first packet, informs the reception of the first packet to the PFC 100, and transmits the header information of the packet to the PFC 100. The PFC 100 sets the flow entry (flow+action) corresponding to the informed header information to the PFS that is an informing source of the first packet.
As described above, in the conventional OpenFlow technique, after any of the PFSs 200 and 300 receives the packet transferred between the HOSTs 400, a transfer control is performed to the packet transmitted and received between the HOSTs 400 by the PFC 100.